<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div:first-child {
            width: 400px;
            height: 400px;
            border: 1px solid red;
            background: linear-gradient(to right, rgba(255, 0, 0, 0) 20%, rgba(255, 0, 0, 1) 50%,
                    rgb(0, 255, 64) 90%)
        }

        .caih {
            width: 500px;
            height: 300px;
            background: repeating-linear-gradient(to right, red 0%, orange 5%, yellow 10%, green 15%,
                    blue 20%, cyan 25%, purple 30%);

        }
    </style>
</head>

<body>
    <div>

    </div>
    <div class="caih"></div>
</body>

</html>